The present invention relates to a method for manufacturing a patterned magnetic recording medium. More particularly, the present invention relates to a method for manufacturing a patterned magnetic recording medium that allows forming an uneven pattern in an interlayer only at required sites with high precision, while realizing excellent recording density in the medium.
Various approaches have been tried to increase the recording density in magnetic recording media such as hard disks or the like. These include, for instance, optimizing materials used in the various constituent members, using finer particles in recording layers, head miniaturization, and adopting perpendicular magnetic recording. These approaches, however, are reaching their limits in terms of enhancing recording density.
With a view to further increasing recording density, therefore, there have been proposed technologies relating to so-called patterned magnetic recording media, such as discrete track media or bit patterned media, in which a fine uneven pattern is worked into a magnetic recording layer.
For example, Japanese Patent Application Laid-open No. 2006-12285 (corresponding to US 2005287397 A1) discloses a recording medium comprising a substrate; a soft magnetic layer formed on the substrate; a recording layer oriented in such a manner so as to have magnetic anisotropy in a direction perpendicular to the surface, formed on the soft magnetic layer, and divided into multiple recording elements in a predetermined uneven pattern; and an interlayer formed between the recording layer and the soft magnetic layer; wherein the recording elements are formed to have a predetermined track shape in a data region.
Japanese Patent Application Laid-open No. 2006-12285 discloses also the feature to the effect that at least part of the intermediate layer in a thickness direction is an orientation film that has properties of enhancing orientability of the recording layer, the orientation film being formed in contact with the recording layer on the substrate side of the recording layer.
Japanese Patent Application Laid-open No. 2006-12285 discloses moreover the feature to the effect that at least part of the intermediate layer in a thickness direction is an etch stop film having a lower etching rate than the recording layer, for a predetermined etching process.
Japanese Patent Application Laid-open No. 2005-50468 (corresponding to US 2006021966 A1) discloses a method for manufacturing a magnetic recording medium, comprising a resist layer processing step of processing a resist layer of an object to be processed to a predetermined pattern shape, the object being obtained by sequentially forming, on a substrate surface, a continuous recording layer, a mask layer and the resist layer; a mask layer processing step of processing the mask layer to the pattern shape, on the basis of the resist layer; a resist layer removal step of removing the resist layer on the mask layer; and a continuous recording layer processing step of processing the continuous recording layer to the above pattern shape, by dry etching based on the mask layer, to divide the continuous recording layer into multiple divided recording elements, wherein the resist layer removal step is performed before the continuous recording layer processing step.
The structures below are conceivable structures for a patterned magnetic recording medium. Specifically, a conceivable structure may comprise a predetermined fine uneven pattern being formed on an interlayer for controlling magnetic domains in a magnetic recording layer, with a granular film being formed over the entire surface of the uneven pattern, and a magnetic recording layer, having magnetic domains oriented in the perpendicular direction, being formed only at the surface of protrusions of unprocessed portions of the interlayer, the protrusions having crystal orientation. Herein, a material containing Ru may be used in the interlayer, the fine uneven pattern may be formed by dry etching or the like, and Co alloy-SiO2 may be used as the granular film.
A desired uneven pattern in the interlayer of such a patterned magnetic recording medium may ordinarily be formed in accordance with a procedure as follows. Firstly, a hard mask layer is formed on the interlayer. Next, a resist is coated onto the hard mask layer, and then the resist is pre-cured, is patterned by nano-imprinting, electron beam exposure or the like, and is cured, to yield a resist pattern. Using this resist pattern, the hard mask is then dry-etched by, for instance, ion beam or reactive ion etching. After stripping of the resist pattern, the exposed surface of the interlayer at portions where the hard mask has been etched is processed by dry etching, for instance, by ion beam or reactive ion etching.
When forming a desired uneven pattern on an interlayer in accordance with the above procedure, the thickness of the interlayer ranges ordinarily from 1 to 20 nm. The interlayer, therefore, is extremely thin, and thus processing may progress down into the soft magnetic layer, below the interlayer, during the step of forming an uneven pattern through dry-etching of the interlayer by ion beam etching, reactive ion etching or the like.
When processing progresses into the soft magnetic layer, the latter is corroded by residues of the reactive gas. This may preclude fully bringing out the inherent characteristics of the soft magnetic layer, namely “to suppress spreading of the magnetic flux generated by the head during recording and to secure sufficient magnetic field in the perpendicular direction”. Such progress results in an excessively large stepped pattern after formation of the magnetic recording layer and the protective layer. Upon filling the recesses of the magnetic recording layer with a non-magnetic material, therefore, it becomes difficult to achieve a flat magnetic recording medium, on account of the resulting filling surface.
The same undesirable effects are encountered when processing the interlayer using the resist pattern alone, employing no hard mask layer.
It is thus extremely difficult to control the depth of the interlayer, down to nanometer units, by dry etching. As a result, even if exposure of the surface of the soft magnetic layer can be detected by plasma emission spectroscopy or the like, processing is still very likely to advance into the soft magnetic layer, unless the level of the recess surface is made highly homogeneous during processing of the interlayer.
Although various technologies relating to patterned magnetic recording media have been proposed, as described above, there is still a need for a manufacturing method of such media in which only necessary sites are processed, with high precision, in a dry etching process during formation of an uneven pattern in an interlayer.
Accordingly, it would be desirable to provide a method for manufacturing a patterned magnetic recording medium that allows forming an interlayer uneven pattern only at required sites, with high precision, while realizing excellent recording density in the medium.